Industrial machinery and control method thereof

ABSTRACT

An industrial machinery includes: a drive mechanism driving a control target that moves work or a tool; a motor; a first sensor detecting a position of the control target; a second sensor detecting a position of the motor; a current controller controlling a supply current to the motor; a servo controller outputting a torque instruction to the current controller; and a numerical controller calculating a processing force of the control target to the work based on position information on the control target acquired from the first sensor, position information on the motor acquired from the second sensor, and the torque instruction, the numerical controller determining that the tool is in failure if an absolute value of a first component of the processing force becomes equal to or larger than a first threshold value while processing the work, the first component having a frequency lower than a predetermined frequency.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2016-223272, filed on Nov. 16,2016, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The embodiments of the present invention relate to an industrialmachinery and control method thereof.

Related Art

An industrial machinery machines work with, for example, a tool attachedto a main shaft. A numerical controlling apparatus (hereinafter, alsoreferred to as an NC (Numerical Controller) apparatus) of the industrialmachinery outputs an instruction to the main shaft to control anoperation of the main shaft and monitors the main shaft torque, or amotor load current. The NC apparatus monitors the main shaft torque todetect failure of the tool used in work processing.

However, for example, if the main shaft torque is small, it is difficultto detect tool failure accurately with the main shaft torque.

In order to detect the tool failure, a sensor to detect a cutting statemay be attached to the industrial machinery. However, in this case, thesensor is additionally required, resulting in a bulky and expensiveindustrial machinery. Another problem is that, once the sensor is infailure, the tool failure cannot be detected.

Accordingly, it is the purpose of the present invention, in order tosolve the above problems, to provide an industrial machinery and amethod of controlling the same, capable of easily and accuratelydetecting the tool failure.

SUMMARY OF THE INVENTION

An industrial machinery according to an embodiment includes: a drivemechanism driving a control target that moves work or a tool; a motoroperating the drive mechanism; a first position sensor detecting aposition of the control target; a second position sensor detecting aposition of the motor; a current controller controlling a supply currentto the motor; a servo controller outputting a torque instruction to thecurrent controller, the torque instruction deciding the supply current;and a numerical controller calculating a processing force of the controltarget to the work based on position information on the control targetacquired from the first position sensor, position information on themotor acquired from the second position sensor, and the torqueinstruction, the numerical controller determining that the tool is infailure if an absolute value of a first component of the processingforce becomes equal to or larger than a first threshold value whileprocessing the work, the first component having a frequency lower than apredetermined frequency.

The numerical controller may determine that the control target is infailure if the absolute value of the first component does not exceed asecond threshold value while processing the work, the second thresholdvalue being smaller than the first threshold value.

An origin of the first component may have an offset based on weight ofthe control target.

The numerical controller may determine that the control target is infailure based on an absolute value of a second component of theprocessing force, the second component having a frequency equal to orhigher than the predetermined frequency.

An industrial machinery according to an embodiment includes: a drivemechanism driving a control target that moves work or a tool; a motoroperating the drive mechanism; a first position sensor detecting aposition of the control target; a second position sensor detecting aposition of the motor; a current controller controlling a supply currentto the motor; a servo controller outputting a torque instruction to thecurrent controller, the torque instruction deciding the supply current;and a numerical controller calculating a processing force of the controltarget to the work based on position information on the control targetacquired from the first position sensor, position information on themotor acquired from the second position sensor, and the torqueinstruction, the numerical controller determining that the tool is infailure based on an absolute value of a second component of theprocessing force, the second component having a frequency equal to orhigher than a predetermined frequency.

The tool may have at least one blade for cutting the work, wherein thedrive mechanism cuts the work while rotating the tool, and the numericalcontroller determines that the tool is in failure if the secondcomponent becomes equal to or larger than a first threshold value duringa term shorter than a period of the second component.

The tool may have a plurality of blades for cutting the work, whereinthe drive mechanism cuts the work while rotating the tool, and thenumerical controller uses the second component to calculate a ratio ofprocessing force of a specific blade to processing force of a firstblade among the plurality of blades and determines that the tool is infailure based on the ratio.

The numerical controller may determine that the tool is in failure if anabsolute value of a difference between the ratio of the specific bladeat a start of processing and the ratio of the specific blade after thestart of processing becomes equal to or larger than a third thresholdvalue.

The numerical controller includes a low-pass filtering function or alow-pass filter circuit, wherein the predetermined frequency is acut-off frequency of the low-pass filtering function or the low-passfilter circuit.

A control method according to an embodiment uses an industrial machineryincluding a drive mechanism driving a control target that moves work ora tool, a motor operating the drive mechanism, a current controllercontrolling a supply current to the motor, a servo controller outputtinga torque instruction to the current controller, the torque instructiondeciding the supply current, and a numerical controller controlling theservo controller. The method includes: calculating a processing force ofthe tool to the work by the numerical controller based on positioninformation on the control target, position information on the motor,and the torque instruction; and determining that the tool is in failureif an absolute value of a first component of the processing forcebecomes equal to or larger than a first threshold value while processingthe work, the first component having a frequency lower than apredetermined frequency.

The numerical controller determines that the control target is infailure based on an absolute value of a second component of theprocessing force, the second component having a frequency equal to orhigher than the predetermined frequency.

A control method according to an embodiment uses an industrial machineryincluding a drive mechanism driving a control target that moves work ora tool, a motor operating the drive mechanism, a current controllercontrolling a supply current to the motor, a servo controller outputtinga torque instruction to the current controller, the servo controllerdeciding the supply current, and a numerical controller to control theservo controller. The method includes: calculating processing force ofthe tool to the work by the numerical controller based on positioninformation on the motor, position information on the control target,and the torque instruction; and determining that the tool is in failurebased on an absolute value of a second component of the processingforce, the second component having a frequency equal to or higher than apredetermined frequency.

The tool may have a plurality of blades for cutting the work, whereinthe drive mechanism cuts the work while rotating the tool, and thenumerical controller uses the second component to calculate a ratio ofprocessing force of a specific blade to processing force of a firstblade among the plurality of blades and determines that the tool is infailure based on the ratio.

The numerical controller may determine that the tool is in failure if anabsolute value of a difference between the ratio of the specific bladeat a start of processing and the ratio of the specific blade after thestart of processing becomes equal to or larger than a third thresholdvalue.

The numerical controller may include a low-pass filtering function or alow-pass filter circuit, wherein the predetermined frequency is acut-off frequency of the low-pass filtering function or the low-passfilter circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of the configuration of a servomotor and a drive mechanism of an industrial machinery according to afirst embodiment;

FIG. 2 is a block diagram showing an example of the configuration of aservo unit, the drive mechanism, and a numerical control apparatusaccording to the first embodiment;

FIGS. 3A to 4B are graphs showing an example of a tool-failuredetermination method according to the first embodiment;

FIGS. 5A to 6B are graphs showing another example of the tool-failuredetermination method according to the first embodiment;

FIGS. 7A and 7B are flowcharts showing a tool-breakage detectionoperation according to the first embodiment;

FIG. 8 is a graph showing an example of a tool failure determinationmethod according to a second embodiment;

FIG. 9 is a flowchart indicating a tool severe-wear detection operationbased on the second component according to the second embodiment;

FIGS. 10A and 10B are graphs showing the second component of the cuttingforce according to the third embodiment; and

FIG. 11 is a flowchart showing a tool breakage detection operationaccording to the third embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will now be explained with reference to the accompanyingdrawings. The present invention is not limited to the embodiments.

First Embodiment

FIG. 1 is a diagram showing an example of the configuration of a servomotor 14 and a drive mechanism 2 of an industrial machinery according toa first embodiment. The servo motor 14 is coupled with the drivemechanism 2 via a coupling 3. The drive mechanism 2 is provided with abed 20, brackets 22, a nut 23, a ball screw 25, bearings 26, a linearguide 27, and a table 28.

The bed 20 is fixed to a main frame of the industrial machinery. On thebed 20, the other components of the drive mechanism 2 are mounted. Thebrackets 22 are fixed on the bed 20 to support the ball screw 25 on bothsides via the bearings 26. The ball screw 25 is coupled with the servomotor 14 via the coupling 3 so as to rotate with the rotation of a shaftof the servo motor 14. The nut 23 has a screw hole to be engaged with ascrew portion of the ball screw 25. The nut 23 can move in an axialdirection of the ball screw 25, as the ball screw 25 rotates. The table28 as a control target is fixed to the nut 23 and is supported by thelinear guide 27. The table 28 moves in the axial direction (in thedirections indicated by an arrow A) of the ball screw 25 and the linearguide 27, as the nut 23 moves. As described, the industrial machinery iscapable of transforming the rotary motion of the servo motor 14 into thelinear motion of the table 28.

The table 28, on which work is mounted, moves the work relative to thebed 20 in order to cut the work with a tool. In this case, the controltarget is a moving object such as the table 28 and the work. Or, insteadof the table 28, the control target may be a tool motor (not shown) forrotating the tool, a chuck with which the tool is attached to the toolmotor, and a main shaft head on which the tool is mounted. In this case,the control target is a moving object such as the table 28, the toolmotor, the chuck, and the tool. The tool is used for processing thework, which is, for example, a drill and an end mill. The drill, the endmill, etc. have at least one blade for cutting the work, capable ofcutting the work with the blade while rotating.

FIG. 2 is a block diagram showing an example of the configuration of aservo unit 1, the drive mechanism 2, and a numerical control apparatus(NC apparatus) 4 according to the present embodiment. The NC apparatus 4is provided with an HMI (Human-Machine Interface) 40, a program supplier41, a program analyzer 42, a route creator 44, a cutting force estimator45, a memory 46, and an error detector 47.

The HMI 40 is an interface between an operator and the numerical controlapparatus 4, which is, for example, a touch panel display. The operatorinputs or selects a processing program on the HMI 40. The HMI 40indicates an operating state of the industrial machinery to the operatoror displays the occurrence of an error when receiving an error signalfrom the error detector 47.

The program supplier 41 acquires a processing program stored in thememory 46 and supplies the processing program to the program analyzer42. The memory 46 is, for example, a ROM (Read Only Memory), a RAM(Random Access Memory), an HDD (Hard Disc Drive) or an SSD (Solid StateDrive). The memory 46 stores a system program for controlling theindustrial machinery entirely, the processing program, parameters forthe industrial machinery, and several types of data. A RAM area in thememory 46 is also used as a loading or working area in execution of thesystem program and the like.

The program analyzer 42 analyses the processing program acquired fromthe memory 46 to generate route creation data. The processing programanalysis gives, for each block of the processing program, thecoordinates of a target position to which a moving part (for example,the table, main shaft head, etc.) of the drive mechanism 2 is to bemoved, a target moving speed of the moving part, etc. The block is abasic unit of the processing program, for example, indicating a one-lineinstruction. One block indicates an instruction for a basic motion, suchas, liner motion, arc motion, main-shaft rotation start/halt, etc. Theroute creation data is generated per block and transferred to the routecreator 44.

Based on the route creation data, the route creator 44 generates aposition instruction per sampling period (control period of the servounit 1). The route creator 44 outputs the position instruction to theservo controller 12 of the servo unit 1. The memory 46, the programanalyzer 42, the route creator 44, the cutting force estimator 45, andthe error detector 47, in the NC apparatus 4, may be integrated into asingle CPU (Central Processing Unit) or configured with separatememories or CPUs.

The servo controller 12 outputs a torque instruction to the currentcontroller 13 per control period in accordance with the positioninstruction. The control period is, for example, about one millisecond.The torque instruction is an instruction for deciding a supply currentto the motor 14. The current controller 13 supplies a current inaccordance with the torque instruction, to the motor 14. The motor 14 isprovided with a rotary encoder 60. The rotary encoder 60, as a secondposition sensor, detects shaft rotation of the motor 14 to measure thetransition of shaft rotary position of the motor 14. The rotary encoder60 feedbacks the transition of shaft rotary position of the motor 14 tothe servo controller 12. Hereinafter, information on the shaft rotaryposition of the motor 14 is referred to as “motor position” and theaction of feed-backing the information is referred to as “motor positionfeed-back”.

As explained with reference to FIG. 1, the motor 14 drives the drivemechanism 2, which causes the table 28 to move along the linear guide27.

The drive mechanism 2 is provided with a linear encoder 50 connected tothe table 28. The linear encoder 50, as a first position sensor,measures the transition of linear position of the table 28. The linearencoder 50 feeds back the transition of linear position of the table 28to the servo controller 12. Hereinafter, information on the linearposition of the table 28 is referred to as “scale position” and theaction of feed-backing the information is referred to as “scale positionfeed-back”.

The servo controller 12 receives the feed-back from the linear encoder50 and the rotary encoder 60 to generate a torque instruction forminimizing an error to instructed positions to control the scaleposition and the motor position.

Furthermore, the torque instruction, the scale position, and the motorposition are fed back to the cutting force estimator 45.

Based on the torque instruction, the scale position, and the motorposition, the cutting force estimator 45 calculates cutting force to thework as the control target. The cutting force as processing force may,for example, be force to press a drill or an end mill against the workwhen the drill or the end mill cuts the work or force that the rotatingdrill or end mill applies to the work. Cutting force Fcut may becalculated by the cutting force estimator 45 that calculates theexpression (1) or (2) in the patent document 1.

$\begin{matrix}{F_{cut} = {{\frac{1}{R}( {{K_{t}I_{a}^{ref}} - {J_{r}{\overset{¨}{\theta}}_{m}}} )} - {M_{t}{\overset{¨}{x}}_{t}} - {\frac{1}{R}T_{fric}} - F_{fric}}} & (1)\end{matrix}$

In the above, the sign Ia (hereinafter, referred to as Ia_ref) havingref as a right-upper appendix is an instructed current value obtainedfrom the torque instruction. The sign xt is the scale position, withdots thereabove indicating two-time time derivative. The sign θm is themotor position (rotation angle), with dots thereabove indicatingtwo-time time derivative. The sign Tfric is friction torque. The signFfric is friction force against the linear motion of the table 28 in thedirection A. The sign Jr is moment of inertia from the motor to the ballscrew. The sign Kt is a torque constant of the motor 14. The sign R is atransformation coefficient between rotary motion components and linearmotion components. The sign Mt is mass of the moving object such as thework and the table 28.

Using friction torque Tfric and friction force Ffric both estimated inadvance and using a low-pass filter for high-frequency noise reduction,an estimated value of the cutting force Fcut is given by the expression(2).

$\begin{matrix}{{\overset{\Cap}{F}}_{cut} = {\frac{g_{cut}}{s + g_{cut}}\lbrack {{\frac{1}{R_{n}}( {{K_{tn}I_{a}^{ref}} - {J_{rn}{\overset{¨}{\theta}}_{m}}} )} - {M_{tn}{\overset{¨}{x}}_{t}} - {\frac{1}{R_{n}}{\overset{\Cap}{T}}_{fric}} - {\overset{\Cap}{F}}_{fric}} \rbrack}} & (2)\end{matrix}$

In the above, the parameters indicating estimated values are given thesign “hat”. The sign “gcut” is a cut-off frequency of a filter in theerror detector 47. The right-lower appendix “n” of each parameterindicates a nominal value.

Among the parameters included in the expressions (1) and (2), theparameters, except for the instructed current value Ia_ref obtained fromthe torque instruction, the scale position xt, and the motor positionθm, are stored in the memory 46 in advance. The memory 46 may be builtin the NC apparatus 4 or provided outside thereof. The parameters may bereceived from the outside of the industrial machinery.

The cutting force estimator 45 applies the torque instruction, the scaleposition and the motor position to the expression (1) or (2) tocalculate cutting force to the work. The cutting force estimator 45receives the torque instruction, the scale position feed-back and themotor position feed-back to calculate the cutting force, per samplingperiod (control period) of the servo controller 12. As described above,the cutting force estimator 45 can estimate cutting force per controlperiod, without using additional sensors such as a force sensor.

The cutting force discussed above includes cutting force of each toolblade, as a second component. Moreover, not only the second component,the cutting force includes a first component which is friction (forexample, the friction torque Tfric and the friction force Ffric),ripples (low-frequency components) due to offset shift in currentfeed-back of the motor 14 in the current controller 13, etc. When usingcutting force including such a variety of frequency-range components, itis difficult for the error detector 47 to accurately detect tool'sbreakage, wear, etc.

Under consideration of above, the error detector 47 according to thepresent embodiment, has a low-pass filtering function or a low-passfilter circuit (for example, a moving average filter) to cutoff a secondcomponent having a predetermined frequency or higher of the cuttingforce, thereby extracting a first component having a frequency lowerthan the predetermined frequency. The predetermined frequency is, forexample, a cutoff frequency of the low-pass filter or the low-passfilter circuit of the error detector 47. The error detector 47determines that the tool is in failure when the first component of thecutting force reaches a first threshold value or larger while processingthe work.

For example, the number of blades of the tool (the number of blades thatcut the same part of the work for each tool rotation) Is denoted as M.The rotation speed of the main shaft for rotating the tool is denoted asN (times of rotation/min). In this case, the peak of cutting force isobserved by P=M×N/60 times per minute. In other words, the secondcomponent of the cutting force appears at about a frequency of P (Hz)during processing. Therefore, with the low-pass filter, the errordetector 47 cuts off the cutting force in a high-frequency rangeincluding or higher than P(Hz) to acquire the first component (thecutting force in a low-frequency range lower than P) of the cuttingforce.

In the present embodiment, a tool failure is determined based on thefirst component of the cutting force. The error detector 47 determinesthe tool failure in real time based on the cutting force per samplingperiod (control period) of the servo controller 12. The tool failuredetermination will be explained later with reference to FIGS. 3A to 4B.

When a tool error is detected, the error detector 47 outputs a haltsignal to the route creator 44 and an error signal to the HMI 40. Onreceiving the halt signal, the route creator 44 halts positioninstruction update, so that the motor 14 and the drive mechanism 2 halt.Together with this, on receiving the error signal, the HMI 40 displaysthe tool failure on a screen, so that a user can realize the toolfailure.

FIGS. 3A to 4B are graphs showing an example of a tool-failuredetermination method according to the present embodiment, the ordinateshowing the first component (N (Newton)) of the cutting force in adrilling direction, and the abscissa showing time. In the presentembodiment, the drive mechanism 2 moves the table 28 in an almosthorizontal direction. Thus, the drive mechanism 2 has, a so-calledhorizontal axis, with zero (N (Newton)) set at the origin Fcenter ofcutting force. In the present embodiment, the NC apparatus 4 performsdrilling to the work in a drill mode. Thus, the tool is a drill. Thedrill mode is specified in an NC program and is used in drilling withthe drill.

FIGS. 3A and 3B show a drill-breakage detection method. The drillbreakage is a failure in which a drill shaft is broken away. The drillmay be broken away while the drill is drilling the work or just at themoment at which the drill is made contact with the work. Even if thedrill is broken away, as long as there is almost no axis centerdeviation between a drill neck portion and a drill tip portion and hencethe neck portion is made contact with the tip portion, the neck portioncontinuously presses the tip portion which is not rotating almost atall. That is, while the drill neck portion is rotating to try tocontinue drilling, the drill tip portion does not rotate almost at alland hence does not cut the work. This results in that, while the work isnot being cut, large cutting force is applied in the drilling forwarddirection.

As shown in FIG. 3A, in the case where the drill is broken away at atime te1 while drilling the work, the cutting force varies normally upto the time te1, and after the time te1, the first component of thecutting force exceeds the upper limit value Fref1 that is the firstthreshold value. When the first component of the cutting force reachesor exceeds the upper limit value Fref1, the error detector 47 determinesthat the tool is in failure and outputs the halt signal and the errorsignal.

As shown in FIG. 3B, in the case where the drill is broken away just atthe moment at which the drill is made contact with the work, at a timete2 immediately after the drill is made contact with the work, the firstcomponent of the cutting force exceeds the upper limit value Fref1. Whenthe first component of the cutting force reaches or exceeds the upperlimit value Fref1, the error detector 47 determines that the tool is infailure and outputs the halt signal and the error signal. The failureshown in FIG. 3B may occur when, for example, the drill blades havealready been worn away, so that the drill cannot drill the work eventhough the drill is made contact with the work. Accordingly, the errordetector 47 may determine that the tool is in failure even only once thefirst component of the cutting force exceeds the upper limit valueFref1.

FIGS. 4A and 4B also show a drill-breakage detection method. Forexample, when the failures shown in FIGS. 3A and 3B are not detected,the drill neck portion moves to drill the next hole, whereas the drilltip portion does not move with the drill neck portion. In this case,axial center deviation occurs between the drill neck portion and thedrill tip portion and hence the neck portion is not made contact withthe tip portion. Therefore, when the drill does not reach the work, asshown in FIG. 4 A, the first component of the cutting force remainssmall and does not exceed the lower limit value Fref2 that is the secondthreshold value. The lower limit value Fref2 is a smaller thresholdvalue than the upper limit value Fref1. For example, when the drill isbroken away in the vicinity of a chuck with which the drill is attachedto a motor, the drill neck portion does not reach the work. Therefore,during work cutting, the first component of the cutting force neverexceeds the lower limit value Fref2. In this case, the error detector 47determines that the tool is in failure. In detail, during work cutting,when the first component of the cutting force never exceeds the lowerlimit value Fref2, the error detector 47 determines that the tool is infailure and outputs the halt signal and the error signal, at a time te3.

Moreover, even if the drill neck portion reaches the work, the drillcannot cut the work. In this case, as shown in FIG. 4B, the firstcomponent of the cutting force becomes equal to or larger than the upperlimit value Fref1. Then, the error detector 47 determines that the toolis in failure and outputs the halt signal and the error signal, at atime te4 at which the first component of the cutting force becomes equalto or larger than the upper limit value Fref1.

As described above, the error detector 47 may determine that the tool isin failure when the first component of the cutting force exceeds theupper limit value Fref1 or never exceeds the lower limit value Fref2,during work cutting.

FIGS. 5A to 6B are graphs showing another example of the tool-failuredetermination method according to the present embodiment. In thisexample, the drive mechanism 2 moves the table 28 in an almostperpendicular direction (almost vertical direction). Thus, the drivemechanism 2 has a so-called vertical axis. In this case, the weight ofmoving objects, such as the tool, the motor for rotating the tool, andthe table 28 is applied downwards because of gravity. In a waiting modewithout cutting, in order to cancel the weight of the moving object bysupporting the moving object in a vertical upward direction, the servounit 1 is required to apply force to the moving object in the verticalupward direction. Therefore, there is an offset at the origin Fcenter inthe vertical upward direction, the offset being almost equal to theweight of the moving object. Provided that the vertical upward directionis a positive direction, the origin Fcenter has a positive offset valuealmost equal to the weight of the moving object, as shown in FIGS. 5A to6B.

It is supposed that the tool cuts the work in a downward direction. Thatis, the drive mechanism 2 applies cutting force in the downwarddirection, with the origin Fcenter as a reference point. Hereinbelow, inFIGS. 5A to 6B, the first component of the cutting force is expressed inabsolute values, with the origin Fcenter as the reference point. Thatis, the first component of the cutting force is the first component ofan absolute value (|Fcenter−F̂cut|) of a difference between the originFcenter and estimated cutting force F̂cut. Even though the origin Fcenteris being offset, the method shown in FIGS. 5A to 6B is basically thesame as the method shown in FIGS. 3A to 4B.

For example, as shown in FIG. 5A, in the case where the drill is brokenaway at a time te11 while drilling the work, the absolute value of thecutting-force first component varies normally up to the time te11, andafter the time te1, exceeds the upper limit value Fref1. When theabsolute value of the cutting-force first component reaches or exceedsthe upper limit value Fref1, the error detector 47 determines that thetool is in failure and outputs the halt signal and the error signal.

As shown in FIG. 5B, in the case where the drill is broken away Just atthe moment at which the drill is made contact with the work, at a timete12 immediately after the drill is made contact with the work, theabsolute value of the cutting-force first component reaches or exceedsthe upper limit value Fref1. When the absolute value of thecutting-force first component reaches or exceeds the upper limit valueFref1, the error detector 47 determines that the tool is in failure andoutputs the halt signal and the error signal. The failure shown in FIG.5B may occur when, for example, the drill blades have already been wornaway, so that the drill cannot drill the work even though the drill ismade contact with the work. Accordingly, the error detector 47 maydetermine that the tool is in failure even only once, during workcutting, the absolute value of the cutting-force first component exceedsthe upper limit value Fref1.

As shown in FIG. 6A, in the case where the drill does not reach thework, the absolute value of the cutting-force first component does notexceed the lower-limit value Fref2. The lower limit value Fref2 is asmaller threshold value than the upper limit value Fref1. For example,when the drill is broken away in the vicinity of a chuck with which thedrill is attached to a motor, the drill neck portion does not reach thework. Therefore, during work cutting, the absolute value of thecutting-force first component never exceeds the lower limit value Fref2.In this case, the error detector 47 determines that the tool is infailure. In detail, during work cutting, when the absolute value of thecutting-force first component never exceeds the lower limit value Fref2,the error detector 47 determines that the tool is in failure and outputsthe halt signal and the error signal, at a time te3.

Moreover, as shown in FIG. 6B, in the case where, even if the drill neckportion reaches the work, the drill cannot cut the work, the absolutevalue of the cutting-force first component reaches or exceeds the upperlimit value Fref1. Then, the error detector 47 determines that the toolis in failure and outputs the halt signal and the error signal, at atime te4 at which the absolute value of the cutting-force firstcomponent becomes equal to or larger than the upper limit value Fref1.As described above, during work cutting, the error detector 47 maydetermine that the tool is in failure when the absolute value of thecutting-force first component exceeds the upper limit value Fref1 ornever exceeds the lower limit value Fref2.

FIGS. 7A and 7B are flowcharts showing a tool-breakage detectionoperation according to the present embodiment.

Firstly, as shown in FIG. 7A, it is determined whether the NC apparatus4 is in a drill mode (S10). The drill mode is a step of drilling workwith a drill as the tool.

One hole is drilled in the work in a one-time drill mode from START toEND in FIGS. 7A and 7B. In the case of drilling a plurality of holes,the drill mode is repeated by the number of holes. If in the drill mode(YES in S10), the error detector 47 acquires estimated cutting forcefrom the cutting force estimator 45. The error detector 47 extracts thefirst component from the cutting force using the filtering function. Theabsolute value of the cutting-force first component is compared with theupper-limit value Fref1 (S20). When the drive mechanism 2 has the axisof gravity, as explained with reference to FIGS. 5A to 6B, there is anoffset equivalent to the weight of the moving object, at the originFcenter of the cutting-force first component. In this case, thecutting-force first component is the first component of an absolutevalue (|Fcenter−F̂cut|) of the difference between the origin Fcenter andthe estimated cutting force F̂cut.

If the absolute value of the cutting-force first component is equal toor larger than the upper-limit value Fref1 (YES in S20), the errordetector 47 determines that the tool is broken away and transmits thehalt signal and the error signal to the route creator 44 and to the HMI40, respectively (S30). On receiving these signals, the route creator 44halts position instruction update and the HMI 40 displays an error onthe screen (S40).

On the other hand, if the absolute value of the cutting-force firstcomponent is smaller than the upper-limit value Fref1 (NO in S20), theerror detector 47 determines that the tool is not broken away. In thiscase, the route creator 44 continuously updates the positioninstruction.

If the drill mode continues (NO in S70), steps S20 to S70 in FIG. 7A arerepeated.

In parallel with the flow of FIG. 7A, the error detector 47 executes theflow shown in FIG. 7B. For example, when the NC apparatus 4 enters thedrill mode in step S10 (YES in S10), the error detector 47 sets a flagFg stored in the memory 46 to zero (555).

Subsequently, the error detector 47 compares the absolute value of thecutting-force first component with the lower-limit value Fref2 (S60). Ifthe absolute value of the first component is smaller than thelower-limit value Fref2 (NO in S60), the error detector 47 continues thedrill mode without changing the flag Fg (NO in S70). If the absolutevalue of the first component is equal to or larger than the lower-limitvalue Fref2 (YES in S60), the error detector 47 changes the flag Fg to 1and continues the drill mode (S65 and NO in S70).

When steps S60 and S70 in FIG. 7B are repeated to finish the drill mode(YES in S70), the error detector 47 checks if the flag Fg in the memory46 is 1 (S80). If the flag Fg is 1 (YES In S80), that is, when theabsolute value of the first component has exceeded the lower-limit valueFref2 even once, the error detector 47 determines that the tool is notbroken away. On the other hand, if the flag Fg is zero (NO in S80), thatis, when the absolute value of the first component has never exceededthe lower-limit value Fref2 during the drill mode, the error detector 47determines that the tool is broken away and transmits the halt signaland the error signal to the route creator 44 and the HMI 40,respectively (S30). On receiving these signals, the route creator 44halts position instruction update in the next drill mode and the HMI 40displays an error on the screen (S40).

In the case where tool breakage is detected, for example, with an errormessage, a message to urge tool replacement is displayed on the HMI 40.With the tool replacement by a user, the NC apparatus 4 can continueprocessing.

The error detector 47 may execute the flows of FIGS. 7A and 7B inparallel. Nevertheless, the error detector 47 may execute either one ofthe flows of FIGS. 7A and 7B after the other.

As described above, the NC apparatus 4 can detect tool breakage usingthe first component of the cutting force. The NC apparatus 4 accordingto the present embodiment performs tool chipping detection with both ofthe upper-limit value Fref1 and the lower-limit value Fref2.Nevertheless, the error detector 47 may perform the tool chippingdetection with either one of the upper-limit value Fref1 and thelower-limit value Fref2.

If tool failure detection like the present embodiment is not performed,tool breakage cannot be accurately detected. If the tool breakage cannotbe accurately detected, holes may not be drilled in the work in themiddle of multiple-hole drilling by an NC-programmed automaticoperation. In this case, continuation of a drilling operation merelyconsumes time and cost for a user.

In contrast, the industrial machinery according to the presentembodiment detects tool breakage using the first component of theestimated cutting force (F̂cut). The second component of the cuttingforce is generated due to cutting by each tool blade and hence variesdue to wear, chipping, etc. of each tool blade. In contrast, the firstcomponent of the cutting force varies due to abnormality or failure suchas breakage of the tool itself, which steadily varies the degree of wearlargely. Therefore, in the present embodiment, abnormality or failuresuch as tool breakage can be accurately and surely detected using thefirst component of the cutting force. In the case of drilling using adrill, the cutting force is force to press the tool against the work,and hence the cutting force includes much more first components thansecond components. In this case, the lower-limit value Fref2 isextremely small and set to a value close to zero.

The present embodiment does not require additional parts (an additionalsensor and the like). Therefore, the industrial machinery according tothe present embodiment is excellent in compactness and cost performance,with no necessity of consideration of failure of additional parts.

Second Embodiment

FIG. 8 is a graph showing an example of a tool failure determinationmethod according to a second embodiment, the ordinate showing cuttingforce including the second component and the first component, and theabscissa showing time. It is a precondition that the drive mechanism 2has a horizontal axis, with zero (N(Newton)) set at the origin Fcenterof the cutting force. In the case where the drive mechanism 2 has theaxis of gravity, the origin Fcenter may be offset, as explained withreference to FIGS. 4A and 4B. Thus, the explanation of the case with theaxis of gravity is omitted here.

For example, a tool having at least one blade, such as an end mill, cutsthe same part of work by the number of blades per rotation. When thenumber of blades is M and the rotation speed at which the tool rotatesis N (times of rotation/min), the second component of the cutting forcehas a waveform with a frequency of P=M×N/60 (Hz) during processing, asexplained above. Therefore, the error detector 47 can acquire the firstcomponent of the cutting force by cutting off the cutting force in ahigh-frequency range including or higher than P(Hz). In FIG. 8, a solidline L2 represents the second component of the cutting force and abroken line L1 represents the first component of the cutting force.

When the tool is cutting normally before a time t20, the secondcomponent having a frequency of P(Hz) appears. However, as the toolsuffers blade wear, the tool cutting performance is lowered. This causeslarger cutting force per blade, which then causes the second componentto be larger. The first component also becomes larger because itincludes a direct current component obtained by passing the secondcomponent through a low-pass filter. Therefore, as the tool suffersblade wear, the first and second components of the cutting force becomegradually larger, as indicated by the lines L1 and L2 of FIG. 8.

As the tool is worn away further, the tool can hardly cut the work,which leads to a larger error in actual-scale positions (position error)to the position instruction. In this case, the industrial machinery mayhalt due to errors. If the state in which tool is worn away further(referred to as severe wear) continues, the tool may be seized at thework, which gives an adverse effect to the quality of the work machinedsurface.

In the second embodiment, in order to detect severe wear of the tool,the error detector 47 measures a term during which the second componentis equal to or larger than the upper-limit value Frefa. If the term islonger than a predetermined term ta, the error detector 47 determinesthat the tool is in failure. The upper-limit value Frefa as the firstthreshold value may be equal to or different from the upper-limit valueFref1 of the first embodiment. The error detector 47 has a timerfunction to measure the term ta.

For example, in the case where the second component is used for failuredetermination, the error detector 47 determines that the tool is infailure when a term from a moment at which L2 shown in FIG. 8 becomesequal to or larger than the upper-limit value Frefa exceeds the term tawithout intermission. In this case, the error detector 47 outputs thehalt signal and the error signal of FIG. 2.

As an option, in the case where the first component of the cutting forceis used in failure determination, the error detector 47 determines thatthe tool is in failure when L1 shown in FIG. 8 becomes equal to orlarger than the upper-limit value Frefa. In this case, the errordetector 47 outputs the halt signal and the error signal of FIG. 2.

The term ta is set to be larger than zero but shorter than a period(1/P) of the second component of the cutting force, as Indicated by anexpression 3.

0<ta<1/P  (expression 3)

Accordingly, with the cutting force including the second component, theerror detector 47 can accurately detect tool failure. Moreover,according to the present embodiment, the error detector 47 canaccurately detect tool failure when the cutting force gradually variesin the case of, for example, tool severe wear.

Failure detection according to the second embodiment may be performed ineach tool cutting direction (X, Y, Z). In this case, upper-limit valuesFrefx, Frefy, and Frefz may be set for the cutting force along anX-axis, a Y-axis, and a Z-axis, respectively. When the number of bladesM of the tool, which are made contact with the work, and also therotation speed N are constant in an X-direction, a Y-direction, and aZ-direction, the term ta may be the same for an X-component, aY-component and a Z-component. When the number of blades M of the tooland/or the rotation speed N are/is different in the X-, Y- andZ-directions, different terms ta may be set for each of the X-, Y- andZ-components.

FIG. 9 is a flowchart indicating a tool severe-wear detection operationbased on the second component according to the second embodiment. In anexample of FIG. 9, the term ta is the same for an X-component, aY-component and a Z-component of the cutting-force second component. Itis defined hereinbelow that the X-, Y- and Z-components are those of thesecond component.

Firstly, the error detector 47 determines whether the X-component,Y-component and Z-component of the cutting force are equal to or largerthan the upper-limit values Frefx, Frefy and Frefz, respectively (S11).If the X-, Y- and Z-components of the cutting force are smaller than theupper-limit values Frefx, Frefy, and Frefz, respectively (NO in S11),the error detector 47 determines that the tool is not in failure. Inthis case, the error detector 47 resets the timer once or puts the timerin a reset mode (S71) and repeats step S11. On the other hand, if anyone of the X-component, Y-component, and Z-component of the cuttingforce is equal to or larger than the upper-limit value Frefx, Frefy orFrefz (YES in S11), the error detector 47 starts the timer function(count-up)(S21).

If the term after any one of the X-, Y- and Z-components of the cuttingforce has surpassed the associated upper-limit value does not exceed theterm ta (NO in S31), the error detector 47 repeats steps S11 to S31. Instep S11, if the X-, Y- and Z-components of the cutting force aresmaller than the upper-limit values Frefx, Frefy and Frefz,respectively, it is determined that the tool is still not in failure,and the error detector 47 resets the timer function (S71) and returns tostep S11. The error detector 47 continues monitoring the cuttingoperation and the cutting force. In essence, the error detector 47determines that the tool is not in failure, if any one of the X-, Y- andZ-components of the cutting force becomes smaller than the associatedupper-limit value before the term after the above one component hassurpassed the associated upper-limit value exceeds the term ta.

On the other hand, if the term after any one of the X-, Y- andZ-components of the cutting force has surpassed the associatedupper-limit value exceeds the term ta with no intermission (YES in S31),the error detector 47 determines that the tool is in failure (severewear) (S41). In this case, the error detector 47 transmits the haltsignal and the error signal to the route creator 44 and the HMI 40,respectively. On receiving these signals, the route creator 44 haltsposition instruction update and the HMI 40 displays an error on thescreen (S61).

On the contrary, if the second component of any one of the X-, Y- andZ-components of the cutting force becomes smaller than the associatedupper-limit value before the term after the second component hassurpassed the associated upper-limit value exceeds the term ta (NO inS31), the error detector 47 determines that the tool is not in failureand returns to step S11 to continue monitoring of the cutting operationand the cutting force. In this case, the error detector 47 resets thetimer function (S71). Accordingly, even if the cutting force containsnoises, the error detector 47 operates without determining tool failure.That is, by setting the term ta, the effect of noises of the cuttingforce can be eliminated.

As described above, the NC apparatus 4 according to the presentembodiment determines that the tool is in failure (severe wear) if theterm after the second component of any one of the X-, Y- andZ-components of the cutting force has surpassed the associatedupper-limit value exceeds the term ta without intermission. In this way,the NC apparatus 4 according to the present embodiment can accuratelyand surely detect tool severe wear. By accurately and surely detectingtool severe wear, it is possible to prevent the industrial machineryfrom being halt due to position errors and the tool from being seized atthe work, thereby maintaining the work machined surface in high quality.

The second embodiment may be combined with the first embodiment.

Third Embodiment

In the first and second embodiments, the NC apparatus 4 performs toolfailure detection using the first component of the cutting force.Different from this, in the third embodiment, the NC apparatus 4performs tool failure detection using the second component of thecutting force. The cutting force may be calculated in the same manner asexplained in the first or second embodiment.

The second component of the cutting force will be explained. If any oneof the tool blades is chipped way or worn away, there is a bigger changein the second component than in the first component, in the cuttingforce. For example, if the tool has many blades and, if one of theblades is chipped way, although there is a small change in the cuttingforce of the entire tool, there is a big change in the cutting force ofthe chipped blade. In this case, it is preferable for the NC apparatus 4to use the second component that represents each blade cutting force,for tool failure detection. Therefore, the NC apparatus 4 eliminates thefirst component containing ripples from the cutting force.

Ripples are, for example, pulsating components contained in a current inthe current controller 13, which is caused by, for example, offset shiftin current feed-back in the current controller 13. Ripples aresuperimposed, as sign waves, on a cutting force waveform in eachrotation of the motor 14, the number of the sign waves corresponding tothe number of pole pairs of the motor 14.

Under consideration of above, the error detector 47 has a low-passfiltering function or a low-pass filter circuit for cutting off afrequency range having a frequency fma or higher. The low-pass filtererallows the cutting force calculated in the first embodiment to passtherethrough. The error detector 47 acquires the first component of thecutting force, which contains low-frequency range ripples. The errordetector 47 eliminates the first component from the cutting force toacquire the second component of the cutting force. That is, the errordetector 47 extracts the first component containing ripples through thelow-pass filter and eliminates the first component from the cuttingforce to acquire the second component of the cutting force.

The cutoff frequency fma of the low-pass filter has a relationship givenby an expression 4.

fm<fma<P  (Expression 4)

Here, fm is a ripple frequency and P is a frequency of the secondcomponent of the cutting force (that is, M×N/60).

According to the above relationship, the error detector 47 extracts thefirst component containing ripples of the cutoff frequency fma or lowerand eliminates the first component from the cutting force to acquire thesecond component having a frequency of P or higher.

Subsequently, a failure detection method using the second component ofthe cutting force will be explained.

FIGS. 10A and 10B are graphs showing the second component of the cuttingforce according to the third embodiment, the ordinate showing the secondcomponent of the cutting force and the abscissa showing time. FIG. 10Ashows cutting force F1 to F4 in an initial state where the tool is justused. FIG. 10B shows cutting force F1_1 to F4_1 after that the cuttingoperation has been performed with the tool for a certain period of time.It is a precondition in the third embodiment that the drive mechanism 2has a horizontal axis, and hence zero (N(Newton)) may be set at theorigin Fcenter of the cutting force. In the case where the drivemechanism 2 has the axis of gravity, the origin Fcenter may be offset,as explained with reference to FIGS. 4A and 4B. Thus, the explanation ofthe case with the axis of gravity is omitted here.

The tool has, for example, four blades that cut the work in eachrotation. In this case, F1 to F4 in FIG. 10A denote cutting forceassociated with the tool's four blades, respectively. In FIG. 10B, F1_1to F4_1 also denote cutting force associated with the tool's fourblades, respectively. In each rotation of the tool, the cutting force F1to F4 or F1_1 to F4_1 are acquired. Since one rotation of the tool is1/P(sec), the cutting force F1 to F4 or F1_1 to F4_1 repeatedly appearat an interval of 1/P.

The tool's blades are in different conditions even in an initial state(new blades). For example, the distance from the tool's rotation centerto each blade tip is little bit different among the blades, and hencethe cut depth is different among the blades. Moreover, a little whileafter the tool is used, the difference among the blade cutting forceF1_1 to F4_1 may become larger. For example, referring to FIGS. 10A and10B, the cutting force F3_1 is extremely smaller than F3 of the initialstate. This indicates that the third one among the four tool blades ischipped away or worn away compared to the others.

Then, the error detector 47 detects tool failure based on the secondcomponent of the cutting force. In detection of the tool failure, theerror detector 47 uses ratios R1, R2 and R3 of the cutting force F2, F3and F4, respectively, to the first-blade cutting force F1, among thecutting force F1 to F4 of the second component. For example, R1, R2, andR3 are given by F2/F1, F3/F1 and F4/F1, respectively.

In this case, the blade initial-state cutting force F1 to F4 areacquired from the second component of the cutting force calculated atthe start of processing. The error detector 47 uses the initial-statecutting force F1 to F4 to calculate F2/F1, F3/F1 and F4/F1, and storesthem as R1, R2 and R3, respectively, in an Internal memory of the errordetector 47 or the memory 46. A ratio (F1/F1=1) of the first-bladecutting force F1 to the first-blade cutting force F1 may also be storedin the memory.

The ratios R1 to R3 indicate variation in the initial-state cuttingforce among the blades. With the ratios, if the cutting force of aspecific blade varies during processing, the error detector 47 candetermine whether it is a change due to wear of the entire blades of thetool (a normal change) or a change due to chipping or extreme wear ofthe specific blade (an abnormal change).

After the start of processing, the error detector 47 uses ratios R1_1 toR3_1 of the cutting force F2_1 to F4_1 to the first-blade cutting forceF1_1, among the cutting force F1_1 to F4_1 of the blades. For example,R1_1, R2_1 and R3_1 are given by F2_1/F1_1, F3_1/F1_1 and F4_1/F1_1,respectively. The error detector 47 uses the cutting force F1_1 to F4_1to calculate F2_1/F1_1, F3_1/F1_1 and F4_1/F1_1, and stores them asR1_1, R2_1 and R3_1, respectively, in the internal memory of the errordetector 47 or the memory 46. A ratio (F1_1/F1_1=1) of the first-bladecutting force F1_1 to the first-blade cutting force F1_1 may also bestored in the memory.

Subsequently, the error detector 47 compares |Ri_1−Ri| with a thresholdvalue S, i being an integer of 1 to 3. The threshold value S, as thethird threshold value, is a positive number of 1 or smaller, stored inthe memory 46 in advance. The threshold value S may, for example, be inthe range from 0.2 to 0.5. If |Ri_1−Ri| is equal to or smaller than thethreshold value S, the error detector 47 determines that the tool is notin failure. If |Ri_1−Ri| becomes larger than the threshold value S, theerror detector 47 determines that the tool is in failure.

For example, when all of the tool blades are worn away almost in thesame degree from the initial state, Ri_1 does not vary from Ri so much.Therefore, |Ri_1−Ri| remains equal to or smaller than the thresholdvalue S. In this case, the error detector 47 determines that the tool isnot in failure. That is, even if there is a variation in the cuttingforce of the blades in the Initial state, if the ratio Ri remainsunchanged during cutting, the error detector 47 determines that the toolis not in failure.

On the contrary, when a specific blade is chipped away or extremely wornaway compared to the other blades, the cutting force of the specificblade becomes extremely smaller than the cutting force of the otherblades. For example, as shown in FIG. 10B, the cutting force F3_1 of thethird blade is extremely smaller than the cutting force F1_1. F2_1 andF4_1 of the other blades. In this case, the third blade may have beenchipped away. The ratio R2_1=F3_1/F1_1 is lowered from R2=F3/F1 verymuch. Therefore, |Ri_1−Ri| becomes larger than the threshold value S. Inthis case, the error detector 47 determines that the tool is in failure.That is, when the ratio Ri_1 of the cutting force of the blades duringcutting shows a big difference from the ratio Ri of the initial state,the error detector 47 determines that the tool is in failure.

The error detector 47 determines that the cutting force F1_1 of thefirst blade is abnormal when every |Ri_1−Ri| becomes equal to or largerthan the threshold value S. This is because, the abnormality of thecutting force F1_1 is related to all of R1_1 to R3_1.

FIG. 11 is a flowchart showing a tool breakage detection operationaccording to the third embodiment.

At the start of processing, the error detector 47 acquires cutting forceestimated by the cutting force estimator 45 (S12). The error detector 47extracts the first component from the cutting force through the low-passfilter and eliminates the first component from the cutting force toacquire the second component (S22).

Subsequently, the error detector 47 calculates the cutting force F1 toF4 of the tool blades from the absolute value of the cutting-forcesecond component. Moreover, the error detector 47 calculates theinitial-state ratios R1 to R3 using the cutting force F1 to F4 (S32).The ratios R1 to R3 are stored in the memory 46 or the internal memoryof the error detector 47.

Thereafter, for each control period, the error detector 47 calculatesthe ratios R1_1 to R3_1 based on the cutting force from the cuttingforce estimator 45, in the same manner as steps S12 to S32 (S42). Theratios R1_1 to R3_1 are also stored in the memory 46 or the internalmemory of the error detector 47. Furthermore, the error detector 47calculates |Ri_1−Ri| (S52) and compares |Ri_1−Ri| with the thresholdvalue S (S62).

If |Ri_1−Ri| is equal to or smaller than the threshold value S (NO inS62), the error detector 47 determines that the tool is not in failureand continues monitoring of the cutting operation and the cutting force.

If |Ri_1−Ri| becomes larger than the threshold value S (YES In S62), theerror detector 47 determines that the tool is in failure (S72). In thiscase, the error detector 47 transmits the halt signal and the errorsignal to the route creator 44 and to the HMI 40, respectively. Onreceiving these signals, the route creator 44 halts position instructionupdate and the HMI 40 displays an error on the screen (S81).

As described above, the NC apparatus 4 according to the third embodimentcalculates the ratios R1 to R3 of processing force of the blades exceptfor the first blade to processing force of the first blade using thesecond component. Then, the NC apparatus 4 determines that the tool isin failure when the absolute value of a difference between the ratios R1to R3 at the start of processing and the ratios R1_1 to R3_1 after thestart of processing, respectively, becomes equal to or larger than thethreshold value S. In this way, the NC apparatus 4 according to thethird embodiment can accurately detect small chipping or wear of eachblade of the tool.

The third embodiment may be combined with the first embodiment and/orthe second embodiment.

At least part of the failure detection method in an industrial machineryaccording to the present embodiment may be configured with hardware orsoftware. When it is configured with software, a program that performsat least part of the functions of the failure detection method may bestored in a storage medium such as a flexible disk and CD-ROM, and theninstalled in a computer to run thereon. The storage medium may not belimited to a detachable one such as a magnetic disk and an optical diskbut may be a standalone type such as a hard disk and a memory. Moreover,a program that achieves at least part of the functions of the failuredetection method may be distributed via a communication network(including wireless communication) such as the internet. The program mayalso be distributed via an online network such as the internet or awireless network, or stored in a storage medium and distributed underthe condition that the program is encrypted, modulated or compressed.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the inventions.

1. An industrial machinery comprising: a drive mechanism driving acontrol target that moves work or a tool; a motor operating the drivemechanism; a first position sensor detecting a position of the controltarget; a second position sensor detecting a position of the motor; acurrent controller controlling a supply current to the motor; a servocontroller outputting a torque instruction to the current controller,the torque instruction deciding the supply current; and a numericalcontroller calculating a processing force of the control target to thework based on position information on the control target acquired fromthe first position sensor, position information on the motor acquiredfrom the second position sensor, and the torque instruction, thenumerical controller determining that the tool is in failure if anabsolute value of a first component of the processing force becomesequal to or larger than a first threshold value while processing thework, the first component having a frequency lower than a predeterminedfrequency.
 2. The industrial machinery according to claim 1, wherein thenumerical controller determines that the control target is in failure ifthe absolute value of the first component does not exceed a secondthreshold value while processing the work, the second threshold valuebeing smaller than the first threshold value.
 3. The industrialmachinery according to claim 1, wherein an origin of the first componenthas an offset based on weight of the control target.
 4. The industrialmachinery according to claim 1, wherein the numerical controllerdetermines that the control target is in failure based on an absolutevalue of a second component of the processing force, the secondcomponent having a frequency equal to or higher than the predeterminedfrequency.
 5. An industrial machinery comprising: a drive mechanismdriving a control target that moves work or a tool; a motor operatingthe drive mechanism; a first position sensor detecting a position of thecontrol target; a second position sensor detecting a position of themotor; a current controller controlling a supply current to the motor; aservo controller outputting a torque instruction to the currentcontroller, the torque instruction deciding the supply current; and anumerical controller calculating a processing force of the controltarget to the work based on position information on the control targetacquired from the first position sensor, position information on themotor acquired from the second position sensor, and the torqueinstruction, the numerical controller determining that the tool is infailure based on an absolute value of a second component of theprocessing force, the second component having a frequency equal to orhigher than a predetermined frequency.
 6. The industrial machineryaccording to claim 5, wherein the tool has at least one blade forcutting the work, wherein the drive mechanism cuts the work whilerotating the tool, and the numerical controller determines that the toolis in failure if the second component becomes equal to or larger than afirst threshold value during a term shorter than a period of the secondcomponent.
 7. The industrial machinery according to claim 5, wherein thetool has a plurality of blades for cutting the work, wherein the drivemechanism cuts the work while rotating the tool, and the numericalcontroller uses the second component to calculate a ratio of processingforce of a specific blade to processing force of a first blade among theplurality of blades and determines that the tool is in failure based onthe ratio.
 8. The industrial machinery according to claim 7, wherein thenumerical controller determines that the tool is in failure if anabsolute value of a difference between the ratio of the specific bladeat a start of processing and the ratio of the specific blade after thestart of processing becomes equal to or larger than a third thresholdvalue.
 9. The industrial machinery according to claim 1, wherein thenumerical controller comprises a low-pass filtering function or alow-pass filter circuit, wherein the predetermined frequency is acut-off frequency of the low-pass filtering function or the low-passfilter circuit.
 10. A control method of an industrial machinerycomprising a drive mechanism driving a control target that moves work ora tool, a motor operating the drive mechanism, a current controllercontrolling a supply current to the motor, a servo controller outputtinga torque instruction to the current controller, the torque instructiondeciding the supply current, and a numerical controller controlling theservo controller, the method comprising: calculating a processing forceof the tool to the work by the numerical controller based on positioninformation on the control target, position information on the motor,and the torque instruction; and determining that the tool is in failureif an absolute value of a first component of the processing forcebecomes equal to or larger than a first threshold value while processingthe work, the first component having a frequency lower than apredetermined frequency.
 11. The method according to claim 10, whereinthe numerical controller determines that the control target is infailure based on an absolute value of a second component of theprocessing force, the second component having a frequency equal to orhigher than the predetermined frequency.
 12. A control method of anindustrial machinery comprising a drive mechanism driving a controltarget that moves work or a tool, a motor operating the drive mechanism,a current controller controlling a supply current to the motor, a servocontroller outputting a torque instruction to the current controller,the servo controller deciding the supply current, and a numericalcontroller to control the servo controller, the method comprising:calculating processing force of the tool to the work by the numericalcontroller based on position information on the motor, positioninformation on the control target, and the torque Instruction; anddetermining that the tool is in failure based on an absolute value of asecond component of the processing force, the second component having afrequency equal to or higher than a predetermined frequency.
 13. Themethod according to claim 12, wherein the tool has a plurality of bladesfor cutting the work, wherein the drive mechanism cuts the work whilerotating the tool, and the numerical controller uses the secondcomponent to calculate a ratio of processing force of a specific bladeto processing force of a first blade among the plurality of blades anddetermines that the tool is in failure based on the ratio.
 14. Themethod according to claim 13, wherein the numerical controllerdetermines that the tool is in failure if an absolute value of adifference between the ratio of the specific blade at a start ofprocessing and the ratio of the specific blade after the start ofprocessing becomes equal to or larger than a third threshold value. 15.The method according to claim 10, wherein the numerical controllercomprises a low-pass filtering function or a low-pass filter circuit,wherein the predetermined frequency is a cut-off frequency of thelow-pass filtering function or the low-pass filter circuit.